The CGDI endorses specifications for several geospatial web services. The specifications fall into the following categories:

• Data visualization: The Web Map Server (WMS) interface specification defines services to create and display superimposed map layers of geographic data from multiple sources.
  
  
• Data presentation: The Styled Layer Descriptor (SLD) specification is a companion specification to the WMS interface specification. It provides some control over how geographic features are to be portrayed, or symbolized.
  
  
• Data storage: The Web Map Context (WMC) Document specification allows for the creation and storage of information (metadata) about maps for re-use. It is also a companion specification to the WMS interface specification.
  
  
• Data manipulation: The Web Feature Service (WFS) specification defines data manipulation operations on geographic features such as water bodies, infrastructures, etc.
  
  
• Data encoding: Geography Markup Language (GML) is an XML coding for the transport and storage of geographic information, including both the geometry and properties of geographic features.
  
  
• Data query: The Filter Encoding specification provides a standard XML-based means of restricting the records that are returned from a query. Filter encoding can handle both spatial and non-spatial aspects of a query.
  
  
• Data access: The GeoData Discovery Service searches geospatial data resource registries, and retrieves metadata about geospatial data. Gazetteers look up geographic regions based on secondary reference systems such as postal codes, CGDI place names, the Canadian Geographic Name Service or the National Topographic Name Service.
  
  
• Data description: The Metadata for Geodata specification provides a standard way of describing geospatial data.

Did you know? More than 200 programs in the Canadian federal government provide map services through the Internet. Click on government maps online for an example of the countless government maps available online.